1. Technical Field
The present invention relates to potassium niobate deposited bodies and methods for manufacturing the same, surface acoustic wave elements, frequency filters, oscillators, electronic circuits, and electronic apparatuses.
2. Related Art
Accompanying the considerable development in the telecommunications field, the demand for surface acoustic wave elements is rapidly expanding. The development of surface acoustic wave elements is directed toward achieving further miniaturization, higher efficiency and higher frequency. In order to achieve this, higher electromechanical coupling coefficient, more stable temperature characteristics and greater surface acoustic wave propagation speed are needed.
It has been found that a single crystal substrate of potassium niobate (KNbO3) (a=0.5695 nm, b=0.3973 nm, and c=0.5721 nm; hereafter this index expression is followed as “orthorhombic crystal”) exhibited a large value of electromechanical coupling coefficient. For example, as described in Jpn. J. Appl. Phys. Vol. 37 (1998) 2929, it was confirmed by experiments that a 0° Y-cut X propagation KNbO3 single crystal substrate (hereafter referred to as a “0° Y—X—KNbO3 substrate”) would exhibit a very large value of electromechanical coupling coefficient reaching as much as about 50%. Also, the same reference reports that the oscillation frequency of a filter using 45° to 75° rotated Y-cut X propagation KNbO3 single crystal substrate (hereafter referred to as a “rotated Y—X—KNbO3 substrate”) exhibited a zero-temperature characteristic around room temperature.
In a surface acoustic wave element that uses a piezoelectric single crystal substrate, its electromechanical coupling coefficient, temperature coefficient, and acoustic velocity define values peculiar to the piezoelectric material used, and are decided according to a cut angle and a propagation direction. 0° Y—X—KNbO3 single crystal substrates exhibit an excellent electromechanical coupling coefficient, but do not exhibit a zero-temperature characteristic like 45° to 75° rotated Y—X—KNbO3 substrates around room temperature. Moreover, the acoustic velocity of a 0° Y—X—KNbO3 single crystal substrate is lower compared to SrTiO3 which is the same perovskite type oxide. Thus, all of the requirements of high electromechanical coupling coefficient, zero-temperature characteristic and high acoustic velocity cannot be satisfied by merely using a KNbO3 single crystal substrate. Moreover, it may be difficult to manufacture a surface acoustic wave element by forming a thin film of potassium niobate on a certain substrate having a large area.